I'm going to take your comment at face value and go with the charitable interpretation that you have sincere beliefs and are sharing them, but I'm also going to explain why doing so is difficult for me and hopefully addressing your points.
It’s not illegal to create digital art (even the disgusting kind) which depicts fictitious grown adults doing grown adult things.
True, but someone with a developmental disability in which they mentally remain very much a child for their whole life is clearly a different thing. I am fairly sure that in the US at least, creating digital art of children being involved in sexual situations is illegal, and as such, I believe by extension that since a developmentally disabled person cannot be considered a "grown adult" that arguably the same should be true for them. (This obviously cannot address the AI-generated amputees, who are "grown adults.")
I would argue that if any such subclass of degenerate exists they already exist.
And I would argue otherwise. There are many, many ideas that I was exposed to throughout my life that had never entered my mental lexicon until the idea was presented to me. Nobody can know everything, and so I don't actually think this is a chicken and egg problem at all. When someone previously has no idea such a thing even exits, and then is presented with such an idea, definitively, one of those things came first.
Secondly, the number of people I have met who genuinely have some pretty fucked up views by ingesting way too much "loli" anime/hentai is way too damn high. I have a very hard time believing that they would have such deeply held views if they didn't have access to such materials.
We have a constitutionally protected right in this country to freedom of expression and that right cannot be infringed simply because you believe that it could lead to more people being taken advantage of
Firstly, not everyone lives in the USA. Secondly, that "constitutionally protected right" has literally been hijacked by "free speech warriors" to infiltrate our government with explicit intent to control speech. That's literally happening right now. Elon Musk is a particularly egregious example of someone deeply hypocritical about this subject, who claims he is a "free speech extremist" and claims that he would never ban any type of speech on his social media... yet does exactly that, literally constantly. I don't feel the need to show as much here because it's well documented elsewhere. He also is literally one of the people infiltrating our government and using keyword filters to delete US history from government websites, so extremely that we lost evidence of the Enola Gay and the Navajo Code Talkers. So while in charge of Xitter, it can be argued he isn't an arm of the government and not restricting free speech on his own website (it can still be argued that his stances don't match his actions) in his position at DOGE, he is literally an arm of the government screeching about "free speech" while simultaneously banning ideas he doesn't like... indiscriminately by keyword, no less.
Once again in regards to not everyone living in the USA, Europe has many different countries which have very strict speech laws, and none of those countries are facing the same loss of human rights and access to historical information that the US is under a so-called free speech supporting government administration. Germany has long has strict rules against Nazi imagery and Nazi speech since the end of World War II and I would not consider Germany to be slipping into fascism because of it. It's arguably something that has held the tide of fascism at bay by refusing to let people try to rewrite history. Musk, for example, regularly uses his free speech to do in regards to World War II, like claiming that Hitler didn't kill anybody, he only ordered others to kill people, and so it's really the evil bureaucrats who followed his orders who were at fault. The man who gave the orders and the bureaucrats are all at fault, in reality, is Musk's argument. Free speech advocates often hide behind it to split hairs and attempt to repaint history in vile ways and I don't personally think having laws that prevent things like, say, holocaust denial, are bad in and of themselves.
How long before the extreme right use that precedent to start prosecuting individuals for other thought crimes?
The extreme right are happily using free speech as a shield to do that literally right now and we are literally in a constitutional crisis because of it. Wake up. Your precious constitution is being abused by so-called free speech activists to limit speech and target the vulnerable, under the guise of "you can't tell us our opinions are wrong." As such, I have a very hard time taking this kind of position at face value because so so so many people hide behind "free speech" as a way to push the most heinous ideas... and it works.
I actually think completely unfettered free speech may be more dangerous than not, but you're welcome to disagree.
EDITS: fixing mistakes, tightening up, removing run-on sentences.